This section provides background information related to the present disclosure which is not necessarily prior art.
As a result of environmental and other concerns, plastic containers, more specifically polyester and even more specifically polyethylene terephthalate (PET) containers are now being used more than ever to package numerous commodities previously supplied in glass containers. Manufacturers and fillers, as well as consumers, have recognized that PET containers are lightweight, inexpensive, recyclable and manufacturable in large quantities.
Blow-molded plastic containers have become commonplace in packaging numerous commodities. PET is a crystallizable polymer, meaning that it is available in an amorphous form or a semi-crystalline form. The ability of a PET container to maintain its material integrity relates to the percentage of the PET container in crystalline form, also known as the “crystallinity” of the PET container. The following equation defines the percentage of crystallinity as a volume fraction:
      %    ⁢                  ⁢    Crystallinity    =            (                        ρ          -                      ρ            a                                                ρ            c                    -                      ρ            a                              )        ×    100  where ρ is the density of the PET material; ρa is the density of pure amorphous PET material (1.333 g/cc); and ρc is the density of pure crystalline material (1.455 g/cc). Once a container has been blown, a commodity may be filled into the container.
Traditionally, stretch blow molding has been used to manufacture resultant containers using a preform. The preform is heated and pressurized gas or fluid is introduced therein to stretch the preform to closely conform to the shape of a mold device. In some applications, the resultant container may shrink due to various mechanical and composition properties of the material being used. In some applications, the mold device can be sized larger than a desired final container size to permit shrinkage of the container into its final shape.
In some cases, containers can be manufactured using a double-blow process. The double-blow process can includes a step where a preform is blown into what is known as a primary article. This primary article is blown in a hot mold and is of similar size, or somewhat larger, than the finished container. In one method, this primary article is then moved through a series of ovens to shrink it to a point smaller than the finished container. In another method, the primary article is removed from the hot mold and allowed to shrink on its own to a point smaller than the actual container. The primary article is then moved into the final blow mold and blown into the finished container. However, according to these processes, the time necessary to either heat the primary article to encourage shrink or the time necessary for the primary article to shrink to a smaller size for final blow molding can delay the overall time of manufacture, thereby reducing the throughput of the manufacturing system. Therefore, there is a need to overcome these disadvantages.